Activation of Defense Mechanisms in the Nudibranchs Peltodoris nobilis and Hermissenda crassicornis

Nudibranchs are marine invertebrates that use various defenses to deter predators. Peltodoris nobilis is a member of the superfamily Doridoidea and uses de novo chemical synthesis for defense. Hermissenda crassicornis is a member of the superfamily Aeolidioidea and uses nematocyst sequestration for defense. Past research explains the function and evolution of defenses in nudibranchs; however, it is unknown whether these defenses are active or passive. The goal of this research was to determine if the defense mechanisms in P. nobilis and H. crassicornis are active or passive and if one method is more effective at preventing predation than the other. It was hypothesized that the activation of defense mechanisms in both nudibranch species was active and that the defenses were equally effective at preventing predation. This hypothesis was tested by comparing the contact times of a juvenile Glebocarcinus oregonensis crab— a predator of nudibranchs—with an anesthetized and non-anesthetized nudibranch. There was no statistical difference in crab contact times between the anesthetized and control P. nobilis nudibranchs; however, the anesthetized H. crassicornis contact times with the crabs were statistically higher than the control. This suggests that the release of chemicals produced de novo in P. nobilis is passive, while the firing of sequestered nematocyst by H. crassicornis is active. The results also indicated that the control H. crassicornis contact times with the crabs were statistically lower than those of P. nobilis; however, the crabs demonstrated little predatory behavior across all trials. Therefore, this study cannot conclusively determine which defense mechanism is more effective at preventing predation.